TIMEMASTER: Adventures in the 4th Dimension (1984)

from the publishers website

In the TimeMaster® time-travel Role-Playing Game, you play an agent of the Time Corps, dedicated to preserving history as it originally occurred. Unfortunately, time keeps changing, due to the blundering of Time Renegades who travel time to live where, when, and how they want and due to the influence of the alien shape-changing Demoreans, who wish to shape all time parallels to their own hideous concept of perfection. Your main tools: a chronoscooter, a "dink" ring, and your own Paranormal Memory of the way things should be. TimeMaster combines the excitement of traditional roleplaying, the problem-solving of a good mystery, and the educational value of public television.

Lurching into action, your battered chronoscooter crosses the void of time and space. Another lurch, and the vertigo fades. The countryside comes into view. Knights in armor battle, clanging sword against shield, and then someone blasts at your neck with a laser beam. Once again, all of Time is a mess, and as an agent of the Time Corps, you must set this world straight or die trying! Adventure to any place, any time, in this universe and beyond! The TimeMaster Roleplaying Game makes you master of the "Fourth Dimension", guiding you to the ultimate adventure in history, legend, and science fiction. fight cunning aliens and savage renegades who twist Time to their own purposes. Only skill and wit stand between the world you know and absolute chaos!